Relator

In a qui tam action, the private party helping the government is called a relator. If the prosecution succeeds, the private party receives a portion of the reward. See False Claims Act.

For example, if an employee of a defense contractor discovered that his boss was defrauding the government, the employee could file a False Claims Actqui tam suit against his employer. In that action, the employee would be the relator, the employer would be the defendant, and the government would be the plaintiff.